65 273 Carter AFB won't start

[RustyRatRod]

Reading it with a vacuum gauge. It shows high vacuum, normal engine after I do get it running and warmed up.
It sure does act like it has a vacuum leak but I think it's not getting enough gas rather than getting too much air. What are possible causes of starving for fuel?

What the hell is "high normal engine"? Vacuum gauges read in graduated measurements marked off in increments of mercury. So where did it read? You're trying to be helped here by several people and giving stupid vague answers is not the way to communicate. Can we have specific numbers, please? Also at what RPM? Idle? 2500? Where?

Thanks.

 

[RichB]

If its not getting fuel try and see it it is pumping to the carb. Is it pumping out of the supply line into the carb? Try to start w/o fuel filter. Check the fuel inlet to the carb body. Pinched metal or rubber fuel line? And the classic, is the linkage opening all the butterflies when you press on the gas pedal? Pressure does not mean volume.

The fuel filter has been checked and swapped out. Linkage I need to check.
I think pressure means the fuel pump is working, but, right, ìt says nothing about flow into the carburetor.

 

[rustycowll69]

worked on a 71 383 Road Runner, years ago, wouldn't run right. In spite of a fresh rebuild, it acted like it was anemic: unsteady idle, not much power, felt lean, and richening it up didn't help much. It took a carb rebuild, shimming the rocker shafts up, and re-regrinding the valves to make it run right. The valve seats were cut by Serdi type cutter, but the seats were on a different centerline than the valve guides, so they weren't sealing properly. The vacuum gauge, and compression test helped figure it out.

 

[RichB]

What the hell is "high normal engine"? Vacuum gauges read in graduated measurements marked off in increments of mercury. So where did it read? You're trying to be helped here by several people and giving stupid vague answers is not the way to communicate. Can we have specific numbers, please? Also at what RPM? Idle? 2500? Where?

Thanks.

In addition to inches of mercury my gauge has segments which are color coded and have descriptions like normal engine,late valve timing, or vacuum leak. I can get more specifics later, but through a range of RPM it points up in the green, normal engine range. I do appreciate the input and suggestions and will be doing many of them.

 

[RustyRatRod]

In addition to inches of mercury my gauge has segments which are color coded and have descriptions like normal engine,late valve timing, or vacuum leak. I can get more specifics later, but through a range of RPM it points up in the green, normal engine range. I do appreciate the input and suggestions and will be doing many of them.

I understand that. Most all of them have color coded areas as well. But giving the description like you have, sounds the same as "timing is good" when someone asks where timing is. If we are going to help you, the lest you can do is provide the most specific answers possible. Thanks.

 

[rustycowll69]

even a sick engine can showe decent vacuum under certain conditions.

 

[RichB]

Another critical area on a 273 is valve lash. Out of adjustment rockers can lead to the symptoms you describe also. Are you sure yours are set correctly.?

Mine are hydraulic lifters with a mild performance cam. I do have one lifter ticking which I hope to adjust. I did make a compression check and it showed normal compression.

 

[RustyRatRod]

even a sick engine can showe decent vacuum under certain conditions.

Zackly wut I was gittin at. lol

 

[BillGrissom]

... I think it's not getting enough gas rather than getting too much air. ...

Kind of the same thing. Both will result in "too lean". Gasoline only ignites in a narrow O/F range, which is why it can frustrate you. In contrast, natural gas or diesel spray ignites very lean (why diesels have no throttle plate). If you do have a vacuum leak, it will idle very fast, assuming it gets the fuel to match. It won't with a carburetor because they match the fuel to the air that flows thru the bore, and doesn't know about a downstream vacuum leak. Many modern FI engines will add the proper fuel to compensate for a vacuum leak. My Mopars are like that. To see, pull the vacuum booster hose to make a massive leak. The engine will run faster, but smooth with no mis-fires. Of course, not true for engines using a mass-air flow sensor (Fords, I think) since the vacuum leak is downstream of that.

With above in mind, when it is idling poorly spray shots of starter fluid down the carburetor bore. If it smooths out, you know the problem is a lean condition. If it idles excessively fast (w/ idle speed screw at normal setting), that indicates a vacuum leak. You can also spray the starter fluid around suspected leak areas (or propane) as a diagnostic. Also, get the Harbor Freight in-line spark tester ($3 on sale) to verify a strong spark. I keep one in the "road bag" of all my vehicles. My 1996 Plymouth was sometimes idling way too fast last summer. I plugged all vacuum taps. I tried propane, but that doesn't work on newer engines since it wasn't running lean (see above). I finally found it by spraying water. Idle speed slowed way down when sprayed at the intake manifold gasket. I found it hard and cracked w/ chunks missing.

 

[moper]

Numbers - we need numbers...
What camshaft? What were the compression results? How many inches of vacuum at idle hot? What rpm? What ignition is in it? What are the voltage readings at the battery, the high side of the resistor, and hot lead to the coil? What is your base ignition timing? Have you verified the installation of the distributor drive and firing order are correct?
"If" the compression is good, and "if" the fuel is getting in there, and "if" the spark is hot and timed properly it will run well. Sounds like you may just need to tweak a few things but the data is what's needed.

 

[AJ/FormS]

At hiway speed, transitioning as you describe, PV circuit.
At 60 mph you may be approaching the max flow of the mains.You got up to 60 without problems, so that circuit is fine. You can take the PV out, put a plug in there, and as long as you don't exceed the ability of the mains to flow, you can probably scoot up to 65 plus mph. But somewhere after 40/50 mph, you need the PV circuit to work to get up to speed reasonably quickly. I found in my combo that at about 10 inches vacuum, the engine wanted the PV to begin flowing. At 30/40, you can still get pretty good acceleration on the mains at 10" vacuum. By 50 it's getting harder, cuz you can only press a little more on the gas and then it goes lean. By 60 you could be nearing the limit of the maincircuit. It will cruise there, but not accelerate. By adding just a teensey bit of throttle at a time,you might even get 70/75mph
I can't figure out why you haven't pulled the bowl off yet,and checked the MJs, and slammed a new PV in there; it's like 10 minutes work.
But then, I also can't figure out why you didn't do a fuelpump output test either, before you put a new pump on there.

 

[65Val]

""You can take the PV out, put a plug in there""

AJ...were talking Carter AFB here...no PV to pull....

 

[RichB]

how much timing do you have ? that makes huge difference to the carb.

About 18 deg. BTDC. Below that it really stumbles.

 

[RichB]

Back to basics
do a compression test.The first shot should be at least 50 or 60 psi.But keep cranking it until you get two consecutive same or near same readings, even if it takes 10 compression cycles, and don't stop in the middle.
Then squirt a small amount of oil into each cylinder. Wind her over for a good 8 seconds, and do another compression test.
Report your results.
If an engine doesn't make good compression, it also won't make proper vacuum, and so the poor old carb can't do it's thing.
If you can't get decent numbers; lash the valves, and try again
Gap your plugs while they're out.

Taking another tack
A brake booster is a prime culprit. It could have an internal leak and you might not be aware of it; while idling clamp the line off, or otherwise plug it. The idle rpm and quality could briefly flutter and then it should return to whatever it was doing prior.
PCVs are another source of trouble. At idle, they're supposed to be a fixed orifice device. Old dirty ones might not be. If the idle vacuum is too low, they will mess you up.
And the sneakiest things are the emulsion tubes in the idle wells. You have to take the clusters out to see them and clean them. While they're out, this is a good time to blow out the idle circuits. Cover the carb with a rag, remove the mixture screws , and have at it. The air should come out of the now-empty cluster pockets, and the rag is there to keep the first slug of fuel from hitting the underside of the hood
And finally....... make sure the secondary air valves are closed up tight but not sticking.
Gaskets and such,you know about. Testing for vacuum leaks,you probably know about.
Good luck

I had the brake booster rebuilt. clamped lines, etc. I finally found that my vacuum leak was due to a bolt in the Edelbrock manifold that did not fit properly. (try finding that one !) My PCV valve is the old original chrome plated one. It seemed to be clear and in working order, but to be safe, I plugged the line for it to the carb. This was all a few months ago.
Can you tell me more about the "emulsion tubes in the idle wells" and how to take them out? By secondary air valves, do you mean the butterflies? Thank you.

 

[BillGrissom]

About 18 deg. BTDC. Below that it really stumbles.

I think that is a sign of "idle too lean". My 1969 Dart slant w/ Holley 1920 used to run like that when it had a plugged idle metering block. Factory spec was ~5 BTDC, but if you gave it more advance, it liked it, even wanting to run away to higher rpm and more advance up to ~20 deg (positive feedback loop - more advance gave more rpm, gave more advance).